1. Field of the Invention
This invention relates to a stencil printer, and more particularly to control of paper supply to a stencil printer.
2. Description of the Related Art
There has been known a stencil printer in which a stencil master is wound around a printing drum and a printing paper is supplied between the printing drum and a press roller which are rotated in contact with each other so that ink supplied inside the printing drum is transferred to the printing paper through the imagewise perforations in the stencil master while the printing paper is conveyed pinched between the printing drum and the press roller.
In such a stencil printer, it is required that the printing paper is supplied between the printing drum and the press roller so that the printing paper is accurately positioned with respect to the stencil master wound around the printing drum. For this purpose, in a conventional stencil printer, paper supply, paper conveyance, printing and paper discharge are effected for each rotation of the printing drum by use of gear mechanisms and/or cam mechanisms which are driven by rotation of the printing drum.
More specifically, the conventional stencil printer comprises a primary paper supply section which feeds out printing papers one by one from a stack of printing papers on a paper supply table, a secondary paper supply section which is provided with a timing roller pair which feeds the printing paper received from the primary paper supply section to between a printing drum and a press roller, a printing section which supplies ink from an ink supply section inside the printing drum to the printing paper which is conveyed pinched between the printing drum and the press roller so that the ink is transferred to the printing paper through a stencil master, and a paper discharge section which discharges the printing paper from the printing drum after printing. A series of actions, paper supply, paper conveyance, printing and paper discharge, are timed on the basis of a detected angular position of the printing drum and a detected position of the printing paper.
In such a conventional stencil printer, printing on one printing paper is done in one rotation of the printing drum irrespective of the length of the printing paper (the dimension as measured in the direction of conveyance of the printing paper). Accordingly, the permissible maximum length of a printing paper basically depends on the circumference of the printing drum, and since the printing actions including paper supply, paper conveyance, printing and paper discharge are controlled detecting the angular position of the printing drum and the position of the printing paper, the permissible maximum length of a printing paper is generally slightly smaller than the circumference of the printing drum.
Recently, there has been a demand for a stencil printer which can print on printing papers which are longer than the permissive maximum length (will be referred to as "overlong printing paper", hereinbelow). In such a case, printing is made only on a part of the printing paper. When printing is to be made on such overlong printing papers, the printing drum completes one rotation before the printing paper is completely discharged from the printing drum, and accordingly, the paper supply action for the next printing paper must be initiated before the preceding printing paper is completely discharged from the printing drum. That is, supply of the next printing paper must be initiated while the trailing end portion of the preceding printing paper is still between the pair of timing rollers or between the printing drum and the press roller.
In the conventional stencil printers, the primary and secondary paper supply sections are generally arranged to convey the printing paper at a speed higher than that at which the printing paper is conveyed by the printing drum and the press roller, and accordingly when supply of a next printing paper is initiated while the trailing end portion of the preceding printing paper is still between the pair of timing rollers or between the printing drum and the press roller, the leading end portion of the next printing paper can collide with the trailing end portion of the preceding printing paper, thereby causing paper jam and the like.